Aman-Jean was a close friend of Georges Seurat; the two artists shared a Paris studio in 1879. Art Historian Robert Herbert called Seurat's portrait of Aman-Jean, "one of the great portrait drawings of the nineteenth century". It was the first work Seurat showed, at the Paris Salon in 1883. Aman-Jean also associated with a range of artists and cultural figures of his era, from Ernest Laurent to Paul Verlaine.
In 1886, he obtained a travelling scholarship and went to Italy, together with Henri-Jean Guillaume Martin and Ernest Laurent; studying the Old Masters. Along with Seurat, he worked as an assistant to Puvis de Chavannes, helping him to realize several of his murals. In 1892, he painted a portrait of the poet, Paul Verlaine, during his convalescence for syphilis at the Hôpital Broussais in the 14th arrondissement of Paris. Verlaine dedicated a sonnet to him and they remained good friends until Verlaine's death in 1896.
He was also one of the first to recognize Joséphin Péladan as an important Artist and exhibited at one of the first showings held at the Salon de la Rose + Croix. Later, he became an important Teacher in his own right; his students included Charles Sydney Hopkinson, Theodor Pallady, and Nicolae Tonitza. In 1923, together with Albert Besnard and Auguste Rodin, he helped create the Salon des Tuileries. Ten years later, he was named a Commander in the Legion of Honour.